IP Multimedia Subsystem (IMS) is the technology defined by the Third Generation Partnership Project (3GPP) to provide IP Multimedia services over mobile communication networks. The architecture and general features of the IMS are described generally in 3GPP specification TS 23.002 and, in more detail, in TS 23.228. IMS provides key features to enrich the end-user person-to-person communication experience through the integration and interaction of services. IMS allows new rich person-to-person (client-to-client) as well as person-to-content (client-to-server) communications over an IP-based network. The IMS makes use of the Session Initiation Protocol (SIP) to set up and control calls or sessions between user terminals (or user terminals and application servers). The Session Description Protocol (SDP), carried by SIP signalling, is used to describe and negotiate the media components of the session. Whilst SIP was created as a user-to-user protocol, IMS allows operators and service providers to control user access to services and to charge users accordingly. Other protocols are used for media transmission and control, such as Real-time Transport Protocol and Real-time Transport Control Protocol (RTP/RTCP).
The IMS is logically structured into a so-called “core network” layer and a so-called “service layer”. The core network layer is implemented by functional entities which are briefly described below. The service layer essentially comprises “Application Servers” arranged to provide services to user terminals (referred to hereinafter as User Equipment (UE)). These Application Servers are connected via the IMS, and/or arranged to mediate in the provision of services by executing specific service-based logic, such as to divert an incoming multimedia session in certain circumstances.
The current IMS standards provide for Communication Barring (CB) services to allow networks to control subscriber access to services. The present state of the 3gpp-standardized CB services in IMS is described in 3GPP TS 24.611. This standard follows and extends the basic principles for call restriction supplementary services in Circuit Switched (CS) and Packet Switched (PS) networks considered in TS 24.088.
TS 24.611 describes in particular the actions of an IMS AS executing CB services on a session initiation request in the event that the request meets the requirements of the CB service provisioned in the profile of the subscriber of the CB service. These service requirements are defined in terms of rules with conditions and actions, which are also defined by the same specification with further references to RFC 4745. In particular, TS 24.611 defines an Incoming Communication Barring (ICB) service that is a service that rejects incoming communications that fulfil certain provisioned or configured conditions on behalf of the terminating user, and an Outgoing Communication Barring (OCB) that is a service that rejects outgoing communications that fulfil certain provisioned or configured conditions on behalf of the originating user. FIG. 1 illustrates this functional architecture schematically, assuming a session being established between two subscribers, UE-A and UE-B, with UE-A being the originating party and UE-B being the terminating party.
The existing specifications do not contain any provisions (relevant to ICB or OCB) for user scenarios other than session initiation. The current approach may create an opportunity for subscribers to circumvent CB services in certain circumstances.